The present invention relates to method and system for forming patterns using a nanoimprint technique. More particularly, the invention relates to a mark position detection system adapted for improvement of alignment accuracy in forming patterns using a nanoimprint technique and to a fine pattern forming system employing this method.
In recent years, finer patterning and higher levels of integration of semiconductor integrated circuits have been in progress. As a pattern printing technology for achieving the fine processing technology, the accuracies of photolithography systems are increasingly progressed. However, the minimum feature size has approached the wavelength of the light source for optical exposure. Also, the lithography technology has approached its limit. Therefore, to achieve still finer patterning and higher accuracy, electron beam writing systems that are one kind of charged particle beam systems have began to be used instead of the lithography technology.
Formation of a pattern using an electron beam adopts a method of consisting of drawing a mask pattern unlike the pattern imaging used in pattern formation employing a light source such as i-line or excimer laser. Therefore, as the number of drawn patterns is increased, the exposure time (drawing time) is increased and hence it takes a long time to form patterns. This is regarded as a drawback. Consequently, as the memory capacity is increased from 256 Mega to 1 Giga and to 4 Giga (i.e., as the scale of integration is increased drastically), the time taken to form patterns is accordingly prolonged drastically. There is the anxiety that the throughput will be deteriorated severely. Accordingly, a cell projection method is being developed to increase the speed of operation of electron beam writing systems. In this method, masks of various shapes are combined and irradiated with an electron beam in a batch mode to form a complexly shaped electron beam. As a result, patterns are made finer but it has become indispensable to increase the size and complexity of the electron beam writing system. There is the disadvantage that the system cost is increased.
In contrast, techniques for forming fine patterns at low cost are disclosed, for example, in the above-cited U.S. Pat. Nos. 5,259,926 and 5,772,905. In particular, a desired pattern is transferred by pressing a mold having the same pattern of nanostructures on its surface as a pattern to be formed on a substrate into a resist film layer formed on the surface of a substrate to which the pattern should be transferred. Especially, according to the nanoimprint technology described in U.S. Pat. No. 5,772,905, a silicon wafer is used as a mold, and fine structures of less than 25 nanometers can be formed by transfer.
Where a fine pattern of a semiconductor integrated circuit or the like is formed, it is necessary to make an accurate alignment, for example, with a reticle or the like on which an original pattern is formed after precisely detecting the pattern position on the substrate placed on a stage. The alignment accuracy needs to be enhanced further as finer patterns are used when the scales of integration of semiconductor devices are increased. For example, in order to form a pattern at the 32-nm node, an accurate alignment is required to be performed with an error less than 10 nm.
When a pattern is formed using a nanoimprint technique, resin is applied to the surface of a substrate to which the pattern will be transferred, and then a mold on which an original pattern has been formed is brought and pressed into contact with the substrate. The mold and substrate are required to be heated or irradiated with UV light. In the prior-art lithography equipment, the reticle on which the original pattern is formed and a plate or substrate on which a pattern will be formed are held in a non-contacting relationship. Under this condition, the pattern is optically transferred. Alternatively, the pattern is transferred by drawing it. Therefore, there is not any factor that produces positioning error where a contact is made when an alignment is made. Meanwhile, in nanoimprinting, contact is unavoidable in principle and so an inexperienced problem will occur. As the resin film suffers from nonuniform deformation in the pressing step, problems take place. For example, light rays used in detecting positions are refracted nonuniformly, resulting in position detection errors. An external force is exerted in a direction different from the pushing direction, producing positional deviation.
Where parallelism is not secured with the substrate to which a transfer is made during the contact and pressing steps, a variation of the thickness of the resin occurs after the transfer. As a result, etching defects are produced in the pattern.